Near-Molecular Hartree—Fock Wavefunction for CH3−

Abstract

Ab initio LCAO—MO—SCF calculations have been performed on CH₃⁻ with a C–H bond length of 1.95 Bohr atomic units, using Gaussian‐type functions (GTF) as the basis set. By successive increases in the size (N) of the basis set of GTF (N = 12, 20, 28, 36, 40) it was possible to approach the estimated molecular Hartree—Fock limit within 0.06 Hartree atomic units. The best calculated total energy was −39.4798 hartrees. The Hartree—Fock limit has been estimated to be −39.535 hartrees for the equilibrium C–H distance, and as high as −39.501 hartrees for the above C–H separation. The variation of the geometry of CH₃⁻ indicated that the molecule is pyramidal in its ground state, with the HCH angle approximately equal to 115°. The inversion‐barrier height is estimated to be 1.22 kcal/mole. The charge distribution, as deduced from Mulliken's population analysis, was such that there was approximately 1.099 negative charge on the carbon atom and 0.033 positive charge on each of the three hydrogen atoms. Due to its symmetry, the planar molecule possessed zero dipole moment but it assumed finite values in pyramidal conformations. The total electron density as well as the near‐Hartree—Fock molecular‐orbital densities are presented in the form of contour maps. Within the framework of a single Slater determinantal wavefunction, estimation for the energy values of some of the low‐lying electronic excited states of CH₃⁻ have been made.